The invention relates to a central lubricating installation, in particular for commercial vehicles, comprising a lubricant reservoir, a pump unit having an electric motor and a pump, a control device controlling interval and running times of the pump unit, a pressure sensor interacting with the control device and monitoring the satisfactory operation of the installation, a pressure limiting valve, and also lubricant lines through which lubricating grease can be delivered to lubricant distributors allocated to lubricating points which are at different distances from the pump unit.
Central lubricating installations of the above type are being increasingly fitted in particular in modern commercial vehicles. They are regularly conceived as consumption lubricating installations and are equipped with so-called Single-line distributors according to DIN 24 271. The control device of the respective installation drives its pump unit at certain time intervals, which can be set by the user, in order to press lubricating grease into the lubricant lines. In the process, metering pistons of lubricant distributors, designed in a conventional manner as post-lubricatinq distributors, are pressurized by a lubricating volume corresponding to their metering size, i.e. they are displaced against the force of a spring in a cylinder allocated to them. As soon as the metering pistons of all distributors are pressurized and a certain value of the pressure in the lubricant line is reached, the pressure sensor signals satisfactory operation of the installation to the control device. In order to obtain an adequate supply to the lubricant distributors even at low temperatures, the pump unit in the known installations works during a firmly preset, comparatively long time, the lubricant quantity which exceeds the receiving capacity of the lubricant distributors during this running time passing back into the lubricant reservoir via the pressure limiting valve after reaching a pressure higher than the response pressure of the pressure sensor. After the pump running time has expired, the pressure in the distribution system is reduced by a relief valve down to a residual pressure, and the lubricating grease is delivered to the lubricating points by the distributor metering pistons, which are under the effect of the spring force.